1. Field of the Invention
The present invention provides a process for producing canthaxanthin by mixing .beta.-carotene with an alkali metal chlorate or an alkali metal bromate in water and an organic solvent immiscible with water; adding an iodine halide or iodine; and adding a metal iodide whereby the .beta.-carotene is oxidized to yield canthaxanthin.
2. Related Art of the Invention
Canthaxanthin, a natural colorant, is used as a food dye and as an additive for animal feeds. A process for producing canthaxanthin is disclosed, for example, in U.S. Pat. No. 4,212,827. In this process .beta.-carotene is oxidized with sodium chlorate or sodium bromate in the presence of iodine, bromine, selenium dioxide, vanadium pentaoxide or osmium tetraoxide as a catalyst.
However, in this production process the time necessary for the reaction is from 1 to 250 hours. Furthermore, in order to obtain canthaxanthin with an optimal yield in an advantageous embodiment, at least 20 hours are required (see column 2, lines 33 to 36 of U.S. Pat. No. 4,212,827). Thus, it is recommended that the reaction is conducted for a long time. As an example in which the reaction time is relatively short, Example 12 in the same United States Patent discloses a process for producing canthaxanthin in which 0.00075 mole of sulfuric acid in 20 ml of water is added dropwise continuously over 2 hours at a temperature of 30.degree. C. into a suspension of 10 g of all-trans-.beta.-carotene in 250 ml of chloroform and an aqueous solution containing 20 g of sodium chlorate and 0.4 g of sodium iodide. The reaction is conducted at the same temperature for 3-4 hours. However, if the reaction mixture becomes strongly acidic in the process of the same Example, the resultant product can decompose. Therefore, this process requires that the addition of sulfuric acid is gradually and carefully performed over a long time.